The problem here is that he is doing that vs UTG range. Do you think he is still doing that with weak hands? Any position stats like how much does he 3bet on the BTN? For the given raise size he is giving out I wouldn't fold either.

But what I would do is that I would Check/Fold the river, what else do you think is Checking the flop when he actually could have bluffed and didn't? And now bets the turn & river what you beat?